This invention is concerned with improvement apparatus provided at underground mine workings. The invention has been devised primarily for the underground mining of coal, particularly by the system known as the "long wall" system. It will however be appreciated that the invention may be applied with advantage to the underground mining of other materials. It also relates to an underground mine working per se at which such apparatus is installed.
In an underground coal mine working of the "long wall" type, a coal-cutting machine is conventionally driven along the upright long wall face being worked by the use of a haulage chain which is anchored at opposite ends of the face. The haulage chain passes over a drive sprocket of the machine, and this sprocket is driven by motor means on the machine whereby the machine hauls itself along the face from one end to the other, and back.
The haulage chain is conventionally 22 millimeter chain and a considerable force is applied to the chain during a hauling and cutting operation of the machine; typically this force is in the order of 20 tonf. This force inevitably stretches the chain, and as the machine traverses along the face an increasing length of slack is established in that part of the chain behind, i.e. at the trailing end of the machine, so that when the machine reaches one end of the face there is then a considerable amount of slack chain behind the machine. When, therefore, the machine is operated to cut in in the reverse direction, the drive sprocket of the machine firstly pulls in the chain slack without appreciable resistance, and when all the slack is pulled in, the chain becomes taut and a shock force is applied to the chain, which results in a shock loading not only of the chain but also of the drive sprocket, in floor means and associated parts. Such shock loading is disadvantageous, in that it increases the risk of breakage of the components. Additionally, the initially slack part of the chain tends to "whip" which may cause damage to other parts of the mining equipment, and could be dangerous to operators in the vicinity.
Several suggestions have been made to reduce this problem. One such suggestion is to anchor the chain at opposite ends of the face to spring or hydraulic rams. However, no prior suggestion has been made which significantly reduces the problem, particularly on long faces, and/or on faces which are curved.